We use the following acronyms in our discussion:
We use the following notations in our discussion.
FIG. 1 shows a general configuration of cellular wireless communication systems. A large geographic area is divided into cells 10. Each cell can be further divided into sectors 12. Typically three sectors per cell are used as shown in the figure. We will use the term sector even when there is only one sector per cell. In each cell, a BS 14, 20, 22 serves three sectors and communicates with multiple MS""s 16, 18 in its cell.
High Data Rate (HDR) is an emerging mobile wireless access technology that enables personal broadband Internet services which can be accessed from anywhere, anytime. Developed by Qualcomm, HDR is a new air interface optimized for IP packet data services. HDR can deliver a shared forward link transmission rate of up to 2.4576 Mbit/s per sector using only (1xc3x97) 1.25 MHz of spectrum. HDR has been adopted by TIA as a new standard in the CDMA2000 family, an EVolution of the current 1xc3x97RTT standard for high-speed data-only (DO) services, formally referred to as 1xc3x97EV-DO or IS-856.
IS-856 defines AN, AT, and sector as follows:
Access Network (AN): The network equipment providing data connectivity between a packet switched data network (typically the Internet) and the access terminals. An access network is equivalent to a base station in the CDMA-2000 standard.
Access Terminal (AT): A device providing data connectivity to a user. An access terminal may be connected to a computing device such as a laptop personal computer or it may be a self-contained data device such as a personal digital assistant. An access terminal is equivalent to a mobile station in the CDMA-2000 standard.
Sector: The part of the access network that provides one CDMA channel.
We will use BS and AN interchangeably and MS and AT interchangeably.
In HDR, the forward-link channel is time-shared among MS""s. Actual forward throughput becomes smaller than the instantaneous rates if there are more than one MS.
The MS periodically monitors the quality of its forward channels by measuring the forward-link SIR values from several sectors. The MS chooses the sector among active sectors whose SIR is the highest and calculates the maximum possible forward-link rate supported at this SIR. The MS then sends a DRC value in every slot (one slot is 1.66 msec) that indicates this rate to the BS. The following table shows the DRC value and the corresponding rate in Kbps. Packet length shows how many slots a forward packet needs at each rate.
In HDR, the reverse link (from MS to BS) can support bit rates 9.6, 19.2, 38.4, 76.8, and 153.6 Kbps in a 1.25 MHz spectrum (no overlap with the forward-link spectrum). Since the reverse link is shared using CDMA, these are the actual rates each MS can get.
A MS can communicate with several sectors. A MS is in soft handoff if decoding of the reverse packet is done at several sectors and an error-free frame, if any, is finally chosen. A MS is in softer handoff, if several sectors in the same cell jointly decode the reverse packet.
Due to the unpredictable nature of the reverse traffic and delay, it is difficult to schedule individual reverse traffic together at the BS. As we will show later, there is a limit on the aggregate reverse rate in each sector at which MS""s can send data reliably. Therefore, it is important to be able to control the reverse rate of each MS so that their aggregate rate rarely exceed the limit. We briefly describe how this is done in HDR.
In HDR, there are four variables for reverse rate control, i.e., MaxRate, CurrentRate, CombindedBusyBit, and CurrentRateLimit. CurrentRate is the actual rate at which a MS sent data last time. The BS can send broadcast (to all MS""s in the sector) or unicast (to a specific MS) RateLimit messages. After receiving the RateLimit message (unicast or broadcast), the MS sets its CurrentRateLimit equal to the RateLimit value. CurrentRateLimit is initially 9.6 Kbps.
The BS can send another broadcast control signal, RAB (reverse activity bit), to all active MS""s. The MS collects all RAB""s from active base stations and determines CombinedBusyBit. The CombinedBusyBit is 1 if any of these RAB""s is 1 and is 0 otherwise. The MS then computes the MaxRate with a certain probability depending on the CombinedBusyBit. This probability is a function of both the CurrentRate and the CombinedBusyBit. The MS then chooses a rate that does not exceed either of MaxRate or CurrentRateLimit. The rate is also limited by the transmission power of the MS (in general more power is needed for transmitting at a higher rate). If the payload size is small enough to be transmitted using a lower rate, then the MS choose the lower rate. The following summarizes the reverse rate variables:
CurrentRateLimit
1. initially 9.6 Kbps
2. after receiving broadcast or unicast RateLimit message, an MS updates it as follows:
a. if the RateLimit less than =CurrentRateLimit, set CurrentRateLimit=RateLimit immediately.
b. if the RateLimit greater than CurrentRateLimit, set CurrentRateLimit=RateLimit after one frame (16 slots).
CombinedBusyBit
1 if and only if any RAB is 1 from any sector.
MaxRate
2.0*CurrentRate if CombinedBusyBit=0 and with probability x.
0.5*CurrentRate if CombinedBusyBit=1 and with probability x.
MaxRate cannot be set to 0 in any case.
MaxRate cannot exceed 153.6 Kbps.
MS selects a transmission rate (becomes CurrentRate) such that
1. rate less than =MaxRate
2. rate less than =CurrentRateLimit
3. rate less than =highest rate that can be accommodated by the transmission power
4. rate less than =highest rate such that the number of minimum payload bits is less than the number of bits to send.
Default values of the transition probability x are:
In general, in one aspect, the invention features a method that includes (a) at a mobile wireless communication device operating in a cell, transmitting data to sectors, and (b) at the base station controlling the reverse data rate of the mobile device based on an estimated amount of interference the mobile device is causing to other sectors. Implementations of the invention may include one or more of the following features. The estimated amount of interference is based on a forward-link SIR for the mobile device. The forward-link SIR is averaged over a period of time. The estimated amount of interference is based on pilot power from the mobile device received at the base station or on total power received from the mobile device at the base station or on the mobile device""s request forward-link data rate. The request data rate is averaged over a certain period of time. The reverse rate of the mobile device is set by the base station. The reverse rate is set as a target rate based on the queue status of the mobile device or on the status of the sector in which the mobile device is operating. The status of the sector comprises a number of mobile devices or a reverse rate of other devices operating in the sector. The reverse rate of the mobile device is set by the mobile device. The reverse rate is set based on a determined rate limit. The rate limit is communicated to the mobile device from the base station. The reverse rate is limited by sending rate control bits from the base station to the mobile device. The mobile device sets a value of MaxRate according to a message from the base station, the MaxRate being dependent on the current rate of the mobile device and given transition probabilities. The mobile device sets a MaxRate deterministically. The aggregate rate from all mobile devices in all sectors is maximized. The rate of each mobile device is restricted by a condition. The condition includes fairness among the mobile devices.
In general, in another aspect, the invention features a method that includes (a) generating one or more reverse rate control bit or bits for each of several mobile devices operating in a sector of a cell, and controlling the reverse rates of the respective mobile devices based on the reveres rate control bits.
In general, in another aspect, the invention features a method that includes (a) at a mobile wireless communication device operating in a sector of a cell, transmitting data to the base station in the sector, and (b) controlling its reverse data rate based on an estimated amount of interference the mobile device is causing to base stations in other sectors. Implementations of the invention may include one or more of the following features. The estimated amount of interference is based on its forward-link SIR. The estimated amount of interference is based on its forward-link rate. The estimated amount of interference is based on its request forward-link data rate. The estimated amount of interference is based on the received power from the base station. The reverse rate is limited by a command from the base station.
Other advantages and features will become apparent from the following description and from the claims.